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Leng X.,Jiangsu University | Zhao Q.,Shanxi Diesel Heavy Industry Co. | Long W.,Dalian University of Technology | Tian J.,Dalian University of Technology | And 4 more authors.
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2014

In order to examine the combustion and emission characteristics of a medium speed marine diesel engine under Miller cycle conditions, three-dimensional computational fluid dynamics (CFD) modeling was used to simulate the in-cylinder work processes. The effects of charge temperature, fuel injection timing and geometric compression ratio were analyzed. The results show that with the decrease of the charge temperature, the ignition delay and the maximum pressure rise rate continuously increase, while both the indicated fuel consumption and NOx emission rate decrease first and then increase. Moreover, under low charge temperature of Miller cycle conditions, retarding the fuel injection timing barely affects the ignition delay, whereas enhancing the geometric compression ratio can evidently shorten the ignition delay. Finally, an optimization of initial charge temperature, injection timing and geometric compression ratio is acquired, leading to 52.4% reduction of NOx emission, without notable penalties in indicated specified fuel consumption. ©, 2014, Central South University of Technology. All right reserved.

Long W.-Q.,Dalian University of Technology | Leng X.-Y.,Dalian University of Technology | Dong Q.,Dalian University of Technology | Du B.-G.,Dalian University of Technology | And 4 more authors.
Dalian Ligong Daxue Xuebao/Journal of Dalian University of Technology | Year: 2011

To explore the feasibility of reducing the NO x emission of a large power marine diesel engine to meet IMO Tier II regulations with low costs by the improvements of the mechanical fuel injection systems, a novel fuel injection system, including the intersecting hole nozzle and pressure-modulating-hole type fuel pump, is developed. Benchmark experiments were performed on a 6PC2-6/2L type marine diesel engine, to clarify the effects of the novel fuel injection systems on NO x emission. The experiment results show that, the fan-shaped spray produced by the intersecting hole nozzle diffuses to such a large scope in the combustion chamber that the leaner mixtures control the combustion temperature, therefore reduce the NO x emission. And the application of the novel fuel injection system to the diesel engine turns out 14.3% reduction of NO x emission and 1.5% reduction of brake specific fuel consumption. It is believed that, with further optimization, the novel fuel injection system has the potential to make the diesel engine meet IMO Tier II regulations.

Leng X.,Jiangsu University | Wei S.,Jiangsu University | Tian J.,Dalian University of Technology | He S.,Dalian University of Technology | And 5 more authors.
Harbin Gongcheng Daxue Xuebao/Journal of Harbin Engineering University | Year: 2014

In order to investigate the influence of charge temperature on the combustion and nitrogen oxide (NOx) emission of a medium speed diesel engine under Miller cycle, three-dimensional computational fluid dynamic modeling was performed to simulate the in-cylinder flow, spray, combustion and NOx formation processes. The simulation results showed that, as the charge temperature decreases, the ignition delay, peak heat release rate of premixed combustion stage, and maximum pressure rise rate continuously increase, especially, at the point when the charge temperature decreases 40 K or more lower than that of the original engine. However, the indicated specific fuel consumption rates and NOx emission rates both decrease first and then increase. The results indicated that the overly lowered charge temperature is not beneficial to the reducing of NOx emission, because the excessively prolonged ignition delay results in too much heat released in the premixed combustion stage, which accelerate the formation of thermal NOx. ©, 2014, Editorial Board of Journal of HEU. All right reserved.

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